1. Field of the Invention
The present invention relates to hydraulic systems that control fluid flow to a hydraulic actuator which produces movement of a mechanical component on a machine, and in particular to preventing the mechanical component from moving in the event of a hydraulic system failure.
2. Description of the Related Art
Construction and agricultural equipment employ hydraulic systems to operate different mechanical elements. For example, a telehandler is a common material handling machine that has a pair of forks or a platform attached to the end of a telescopic boom pivotally coupled to a tractor. Separate hydraulic actuators are utilized to raise and lower the boom, vary the boom length, and tilt the forks or platform, with each of those operations being referred to as a “hydraulic function” of the machine. “Hydraulic actuator”, as used herein, generically refers to any device, such as a cylinder-piston arrangement or a motor, that converts hydraulic fluid flow into mechanical motion.
The operator of the machine sits in a cab and manipulates levers or joystick to control the hydraulic actuators and thus the mechanical components of the machine. That manipulation operates valves that govern the flow of fluid from a pump to the hydraulic actuators. The valves may be located near the cab or elsewhere on the machine and are connected to the hydraulic actuators by hoses. Even when a valves are located relatively close to the associated hydraulic actuator hoses still are used.
The hoses on construction and agricultural equipment are exposed to physical abuse and harsh environmental conditions which results in deterioration that leads a hose bursting. When a hose between the valve assembly and the hydraulic actuator bursts, the fluid within the actuator is able to rapidly escape. If the ruptured hose is connected to a machine component that carries a heavy load, such as the boom of a telehandler or excavator, that rapidly escaping fluid may allow that component to drop precipitately resulting in damage or injury.
Therefore, it is desirable to provide a mechanism that prevents motion of a machine component upon failure of a hydraulic component connected thereto.